It is sometimes desirable for tires to have a combination of good wet skid resistance, low rolling resistance, tear strength, and good wear characteristics. Wear characteristics of a tire tread are often difficult to improve without sacrificing traction and/or rolling resistance. In one aspect, such properties depend upon dynamic viscoelastic properties of the tire tread rubber composition and the rubbery polymers utilized in the rubber composition.
In order to reduce the rolling resistance and to improve the tread wear characteristics of tires, rubbers or rubbery polymers having a high rebound physical property (low hysteresis) have often been used for the tire tread rubber compositions. However, in order to increase the wet skid resistance of a tire tread, rubbery polymers that have a relatively lower rebound physical property (higher hysteresis) which thereby undergo a greater energy loss have sometimes been used for such tread rubber compositions. In order to achieve such relatively inconsistent viscoelastic properties for the tire tread rubber compositions, blends (mixtures) of various types of synthetic and natural rubbers are normally utilized in tire treads.
It is often desirable for synthetic rubber polymers to exhibit relatively low levels of hysteresis (indicated by relatively higher rebound values). This is usually particularly important in the case of elastomers that are used in tire tread rubber compositions. In practice, the elastomers are conventionally blended with a sulfur curative, rubber reinforcing fillers such as, for example, precipitated silica and rubber reinforcing carbon black, sulfur vulcanization accelerators, rubber antidegradants and other desired rubber chemicals and are then subsequently vulcanized, or cured, under pressure at an elevated temperature in a suitable mold. The physical properties of such cured rubber compositions depend upon the degree to which the rubber reinforcing fillers, such as carbon black or silica, are homogeneously dispersed throughout the elastomer. The degree of homogeneity of the dispersement of the reinforcing filler relates, at least in part, to the degree of affinity that carbon black or silica for the rubbery polymer.
Amorphous silica reinforcement has sometimes been used in combination with rubber reinforcing carbon black to promote lower rolling resistance (e.g. better vehicular fuel economy) and to promote better traction (e.g. skid and braking resistance) for a tire tread rubber composition. However, use of such silica reinforcement filler, as compared to rubber reinforcing carbon black, often results in a decrease in wear resistance (e.g. increase in tread wear) of a tire tread rubber composition.
Accordingly, it is envisioned that use of a combination amorphous silica (e.g. precipitated silica) and rubber reinforcing carbon black might be used to balance the challenges of promoting reduced tread wear (e.g. increased abrasion resistance of the rubber composition), reduced tire rolling resistance (e.g. increased rebound values of the rubber composition) as well as promoting traction for the tire tread instead of using carbon black or silica separately as reinforcing filler.
In one aspect, terminal modified or functionalized elastomers, which promote an interaction with a wide variety of such silica and carbon black reinforcing fillers to promote good dispersibility of such reinforcing fillers within the rubber composition, and thereby suitable wear resistance (e.g. suitable abrasion resistance) of the rubber composition, might be used.
Accordingly, functionalized rubber polymers (elastomers) and methods of making same for use in rubber compositions, such as for use in tires, are needed.